For two of the most powerful men in the United States, Donald Trump and John Roberts, it has been a delicate dance from the start. 

In 2015, the man who would become the chief executive of the United States assailed the integrity of its chief justice, calling Roberts "disgraceful" and "disappointing" - and, later, an "absolute disaster" - for earlier upholding the Affordable Care Act, the Obamacare law that Trump subsequently sought to repeal. 

A little more than a year later on the U.S. Capitol steps, Roberts, an enigmatic conservative Supreme Court justice from the American Midwest, swore in Trump, a brash businessman-turned-politician from New York City, as president. Any lingering tension had evaporated under smiles, handshakes and a backdrop of applause. 

Since then, the dynamic between the two has remained complicated, marked by dramatic legal wins for Trump as well as painful losses, and punctuated by clashes between the two as Trump shattered norms by aggressively pushing his policies while brooking little dissent - including from the coequal branch of government that Roberts leads: the judiciary. 

The tension has risen once again, culminating in an extraordinary public statement by Roberts on Tuesday rebuking the Republican president for urging the impeachment of a Washington-based federal judge who faulted the administration's actions in a dispute over the legality of deportation flights.

"For more than two centuries," Roberts said, "it has been established that impeachment is not an appropriate response to disagreement concerning a judicial decision."

For Roberts, who is seen as deeply conservative but also concerned about the institutional credibility and perception of the Supreme Court, chastising Trump puts him in a difficult spot. It has drawn sharp criticism from Trump's allies and comes as the court braces for the flood of legal challenges to Trump's myriad executive actions.

'A CERTAIN MEASURE OF CONTEMPT'

"I suspect Roberts has a certain measure of contempt for Trump and the way he treats judges," said University of Michigan law professor Richard Friedman, a Supreme Court historian. "Roberts is an establishment Republican, but I think he's horrified." 

While Roberts and Trump often may converge on legal and substantive goals, there are sharp divergences emerging, according to University of Chicago constitutional law expert Aziz Huq. 

Through his flurry of executive actions to shutter federal departments, fire thousands of federal employees, tar...